Memory device supporting a high-efficient input/output interface and a memory system including the memory device

ABSTRACT

A memory system including: a memory controller to transmit a command, an address, or data to a first channel based on a data input/output signal having one of N (N is a natural number of three or more) different voltage levels during a first time interval, the memory controller transmitting the command, the address, or the data not transmitted during the first time interval to the first channel based on the data input/output signal having one of two different voltage levels during a second time interval; and a memory device to sample the data input/output signal received via the first channel during the first time interval in a pulse amplitude modulation (PAM)-N mode, the memory device sampling the data input/output signal received via the first channel during the second time interval in a non return to zero (NRZ) mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2020-0134639, filed on Oct. 16, 2020 in the KoreanIntellectual Property Office, the disclosure of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The inventive concept relates to a memory device, and more particularly,to a memory device supporting a high-efficient input/output interfaceand a memory system including the memory device.

DISCUSSION OF RELATED ART

Recently, storage devices such as solid state drives (SSDs) have beenwidely used. SSDs have quick access time and low latency and their cellsmay contain multiple bits of data. A storage device may include a memorydevice such as a flash memory and a memory controller for controllingthe memory device. The memory device may transceive input/output signalsto and from the memory controller via certain pins. For example, thememory device may receive a command, an address, and data from thememory controller in a data input/output signal (DQ) transmitted via aDQ pin. According to this input/output interface, the efficiency thereofmay vary according to the transmission time of commands, addresses, anddata. Accordingly, to increase the efficiency of the input/outputinterface between the memory device and the memory controller, a newsignaling method for data input/output signals may be employed.

SUMMARY

An embodiment of the inventive concept provides a memory systemincluding: a memory controller configured to transmit a command, anaddress, or data to a first channel based on a data input/output signalhaving one of N (N is a natural number of three or more) differentvoltage levels during a first time interval, the memory controllerconfigured to transmit the command, the address, or the data nottransmitted during the first time interval to the first channel based onthe data input/output signal having one of two different voltage levelsduring a second time interval; and a memory device configured to samplethe data input/output signal received via the first channel during thefirst time interval in a pulse amplitude modulation (PAM)-N mode, thememory device configured to sample the data input/output signal receivedvia the first channel during the second time interval in a non return tozero (NRZ) mode.

An embodiment of the inventive concept provides a memory deviceincluding: a receiver configured to output M bits (M is a natural numberof two or more) corresponding to a voltage level of a data input/outputsignal received via a data input/output signal pin (DQ pin) based onfirst through (N−1)^(th) (N is a natural number of three or more)reference voltages in a PAM-N mode, and output one bit corresponding tothe voltage level of the data input/output signal based on a certainreference voltage of the first through (N−1)^(th) reference voltages inan NRZ mode; and a control logic circuit configured to control thereceiver in the PAM-N mode or the NRZ mode based on a symbol type of thedata input/output signal corresponding to one of a command, an address,and data.

An embodiment of the inventive concept provides a memory systemincluding: a memory controller configured to transmit to a first channela data input/output signal having one of two different voltage levels orthe data input/output signal having one of N (N is a natural number ofthree or more) different voltage levels, according to a symbol type ofthe data input/output signal corresponding to one of a command, anaddress, and data; and a memory device configured to sample the datainput/output signal in an NRZ mode or a PAM-N mode according to thesymbol type of the data input/output signal received via the firstchannel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive concept will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a block diagram of a memory system according to an embodimentof the inventive concept;

FIG. 2 is a block diagram of a memory system according to an embodimentof the inventive concept;

FIG. 3 illustrates the memory system of FIG. 2 for exchanging datainput/output signals, according to an embodiment of the inventiveconcept;

FIG. 4A is a graph illustrating an example of a data eye for describinga four-level pulse amplitude modulation (PAM-4) method of the datainput/output signals, according to an embodiment of the inventiveconcept;

FIG. 4B is a graph illustrating an example of a data eye for describinga non-return to zero modulation (NRZ) method of the data I/O signals,according to an embodiment of the inventive concept;

FIGS. 5A, 5B, 5C and 5D illustrate signaling methods of the data I/Osignals, according to an embodiment of the inventive concept;

FIG. 6 is a flowchart of an example operation of the memory device inFIG. 3, according to the signaling method of FIG. 5A;

FIG. 7A is an example timing diagram for a program operation, accordingto the embodiment of FIG. 5A;

FIG. 7B is an example timing diagram for a read operation, according tothe embodiment of FIG. 5A;

FIG. 8 is an example block diagram of the memory device in FIG. 2;

FIG. 9 is a diagram of examples for generating mode signals in FIG. 8;

FIG. 10 is a block diagram of an example of a transmitter, according toan embodiment of the inventive concept;

FIG. 11A illustrates an example operation of the transmitter in FIG. 10in a PAM-4 mode;

FIG. 11B illustrates an example operation of the transmitter in FIG. 10in an NRZ mode;

FIG. 12 is an example circuit diagram of a first driver and a seconddriver in FIG. 10;

FIG. 13 is a block diagram of an example of a receiver, according to anembodiment of the inventive concept;

FIG. 14 is a diagram of an example operation of the receiver of FIG. 13;

FIG. 15A is a timing diagram of an example operation of the registercircuit in FIG. 13 in a PAM-4 mode;

FIG. 15B is a timing diagram of an example operation of the registercircuit in FIG. 13 in an NRZ mode;

FIG. 16 is an example block diagram of the register circuit in FIG. 13;

FIG. 17 is a block diagram of a solid state drive (SSD) system to whicha memory device is applied, according to an embodiment of the inventiveconcept; and

FIG. 18 is a block diagram of a network system to which a memory systemis applied, according to an embodiment of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the inventive concept will be describedclearly and in detail so that one of ordinary skill in the art canimplement the inventive concept.

FIG. 1 is a block diagram of a memory system according to an embodimentof the inventive concept. Referring to FIG. 1, a memory system 10 mayinclude a memory device 100 and a memory controller 200. The memorysystem 10 may support first through m^(th) channels CH1 through CHm, andthe memory device 100 may be connected to the memory controller 200 viathe first through m^(th) channels CH1 through CHm. For example, thememory system 10 may be a storage device such as a solid state drive(SSD).

The memory device 100 may include a plurality of memory devices NVM11through NVMmn. Each of the plurality of memory devices NVM11 throughNVMmn may be connected to one of the first through m^(th) channels CH1through CHm via a corresponding way. For example, memory devices NVM11through NVM1 n may be connected to the first channel CH1 via ways W11through W1 n, memory devices NVM21 through NVM2 n may be connected to asecond channel CH2 via ways W21 through W2 n, and memory devices NVMm1through NVMmn may be connected to an m^(th) channel CHm via ways Wm1through Wmn. In an embodiment of the inventive concept, each of theplurality of memory devices NVM11 through NVMmn may be implemented in amemory unit capable of operating according to an individual command fromthe memory controller 200. For example, each of the plurality of memorydevices NVM11 through NVMmn may be a chip or die, but the inventiveconcept is not limited thereto.

The memory controller 200 may transceive signals to and from the memorydevice 100 via the first through m^(th) channels CH1 through CHm. Forexample, the memory controller 200 may transmit commands CMDa throughCMDm, addresses ADDRa through ADDRm, and data DATAa through DATAm to thememory device 100 via the first through m^(th) channels CH1 through CHm,or may receive the data DATAa through DATAm from the memory device 100via the first through m^(th) channels CH1 through CHm.

The memory controller 200 may select one of memory devices connected toa channel, and transceive signals to and from the selected memorydevice. For example, the memory controller 200 may select the memorydevice NVM11 of the memory devices NVM11 through NVM1 n connected to thefirst channel CH1. The memory controller 200 may transmit the commandCMDa, the address ADDRa, and the data DATAa to the selected memorydevice NVM11 via the first channel CH1, or may receive the data DATAafrom the selected memory device NVM11 via the first channel CH1.

The memory controller 200 may transceive signals to and from the memorydevice 100 in parallel via different channels. For example, while thememory controller 200 transmits the command CMDa to the memory device100 via the first channel CH1, the memory controller 200 may transmitthe command CMDb to the memory device 100 via the second channel CH2.

The memory controller 200 may control the overall operation of thememory device 100. The memory controller 200 may control each of theplurality of memory devices NVM11 through NVMmn respectively connectedto the first through m^(th) channels CH1 through CHm by transmittingsignals to the first through m^(th) channels CH1 through CHm. Forexample, the memory controller 200 may control a selected one of thememory devices NVM11 through NVM1 n by transmitting the command CMDa andthe address ADDRa to the first channel CH1.

Each of the first through m^(th) channels CH1 through CHm may operateunder the control of the memory controller 200. For example, the memorydevice NVM11 may program the data DATAa according to the command CMDa,the address ADDRa, and the data DATAa provided via the first channelCH1. For example, the memory device NVM21 may read the data DATAbaccording to the command CMDb and the address ADDRb provided via thesecond channel CH2, and may transmit the read data DATAb to the memorycontroller 200 via the second channel CH2.

In FIG. 1, it is illustrated that the memory device 100 communicateswith the memory controller 200 via m channels, and the memory device 100includes n memory devices corresponding to each channel. However, thenumber of channels and the number of memory devices connected to onechannel may be variously changed.

FIG. 2 is a block diagram of a memory system according to an embodimentof the inventive concept. Referring to FIG. 2, a memory system 20 mayinclude a memory device 300 and a memory controller 400. The memorydevice 300 may correspond to one of the plurality of memory devicesNVM11 through NVMmn communicating with the memory controller 200 throughone of the first through m^(th) channels CH1 through CHm in FIG. 1. Thememory controller 400 may correspond to the memory controller 200 inFIG. 1.

The memory device 300 may include first through eighth pins P11 throughP18, a memory interface circuit (I/F) 310, a control logic circuit 320,and a memory cell array 330.

The memory I/F 310 may receive a chip enable signal nCE from the memorycontroller 400 via the first pin P11. The memory I/F 310 may transceivesignals to and from the memory controller 400 via the second througheighth pins P12 through P18 according to the chip enable signal nCE. Forexample, when the chip enable signal nCE is in an enable state (forexample, a low level), the memory I/F 310 may transceive signals to andfrom the memory controller 400 via the second through eighth pins P12through P18.

The memory I/F 310 may receive a command latch enable signal CLE, anaddress latch enable signal ALE, and a write enable signal nWE from thememory controller 400 via the second through fourth pins P12 throughP14. The memory I/F 310 may receive a data input/output signal DQ fromthe memory controller 400 via the seventh pin P17, or may transmit thedata input/output signal DQ to the memory controller 400 via the seventhpin P17. A command CMD, an address ADDR, and data DATA may betransmitted by using the data input/output signal DQ. For example, thedata input/output signal DQ may be transmitted via a plurality of signallines. In this case, the seventh pin P17 may include a plurality of pinscorresponding to a plurality of data input/output signals DQ.

The memory I/F 310 may obtain the command CMD from the data input/outputsignal DQ that is received during an enable period (for example, a highlevel state) of the command latch enable signal CLE, based on toggletimings of the write enable signal nWE. The memory I/F 310 may obtainthe address ADDR from the data input/output signal DQ that is receivedduring the enable period (for example, a high level state) of theaddress latch enable signal ALE, based on toggle timings of the writeenable signal nWE.

In an embodiment of the inventive concept, the write enable signal nWEmay maintain a toggle-off state (for example, a high level or a lowlevel state), and then, may toggle between the high level state and thelow level state. For example, the write enable signal nWE may be toggledin a period in which the command CMD or the address ADDR is transmitted.Accordingly, the memory I/F 310 may obtain the command CMD or theaddress ADDR based on toggle timings of the write enable signal nWE.

The memory I/F 310 may receive a read enable signal nRE from the memorycontroller 400 via the fifth pin P15. The memory I/F 310 may receive adata strobe signal DQS from the memory controller 400 via the sixth pinP16 or may transmit the data strobe signal DQS to the memory controller400 via the sixth pin P16.

In the data DATA output operation of the memory device 300, the memoryI/F 310 may receive the read enable signal nRE that toggles via thefifth pin P15, before outputting the data DATA. The memory I/F 310 maygenerate the data strobe signal DQS that toggles in response to togglingof the read enable signal nRE. The memory I/F 310 may transmit the datainput/output signal DQ including the data based on a toggle timing ofthe data strobe signal DQS. Accordingly, the data DATA may be alignedwith the toggle timing of the data strobe signal DQS and transmitted tothe memory controller 400.

In a data input operation of the memory device 300, when the datainput/output signal DQ including the data DATA is received from thememory controller 400, the memory I/F 310 may receive from the memorycontroller 400 the data strobe signal DQS toggling together with thedata DATA. The memory I/F 310 may obtain the data DATA from the datainput/output signal DQ based on the toggle timing of the data strobesignal DQS. For example, the memory I/F 310 may obtain the data DATA bysampling the data input/output signal DQ at rising and falling edges ofthe data strobe signal DQS.

The memory I/F 310 may transmit a ready/busy output signal nR/B to thememory controller 400 via the eighth pin P18. The memory I/F 310 maytransmit state information of the memory device 300 to the memorycontroller 400 via the ready/busy output signal nR/B. When the memorydevice 300 is in a busy state (e.g., when internal operations of thememory device 300 are being performed), the memory I/F 310 may transmitthe ready/busy output signal nR/B indicating a busy state to the memorycontroller 400. When the memory device 300 is in a ready state (e.g.,when internal operations of the memory device 300 are not performed orare completed), the memory I/F 310 may transmit the ready/busy outputsignal nR/B indicating a ready state to the memory controller 400.

The control logic circuit 320 may control various operations of thememory device 300. The control logic circuit 320 may generate controlsignals for controlling other components of the memory device 300according to a command and/or address CMD/ADDR obtained from the memoryI/F 310. For example, the control logic circuit 320 may generate variouscontrol signals for programming the data DATA into the memory cell array330, or reading the data DATA from the memory cell array 330.

The memory cell array 330 may store the data DATA obtained from thememory I/F 310 under the control of the control logic circuit 320. Thememory cell array 330 may output the stored data DATA to the memory I/F310 under the control of the control logic circuit 320.

The memory cell array 330 may include the plurality of memory cells. Forexample, the plurality of memory cells may include flash memory cells.However, the inventive concept is not limited thereto, and the memorycells may include resistive random access memory (RAM) (RRAM) cells,ferroelectric RAM (FRAM) cells, phase change RAM (PRAM) cells, thyristorRAM (TRAM) cells, magnetic RAM (MRAM) cells, and dynamic RAM (DRAM)cells. Hereinafter, embodiments of the inventive concept will bedescribed focusing on an example in which the memory cells include NANDflash memory cells.

The memory controller 400 may include first through eighth pins P21through P28, and a controller interface circuit (I/F) 410. The firstthrough eighth pins P21 through P28 may correspond to the first througheighth pins P11 through P18 of the memory device 300, respectively. Inother words, the first pin P21 may be connected to the first pin P11 andthe eighth pin P28 may be connected to the eighth pin P18.

The controller I/F 410 may transmit the chip enable signal nCE to thememory device 300 via the first pin P21. The controller I/F 410 maytransceive signals to and from the memory device 300 selected by usingthe chip enable signal nCE via the second through eighth pins P22through P28.

The controller I/F 410 may transmit the command latch enable signal CLE,the address latch enable signal ALE, and the write enable signal nWE tothe memory device 300 via the second through fourth pins P22 throughP24. The controller I/F 410 may transmit the data input/output signal DQto the memory device 300 via the seventh pin P27, or may receive thedata input/output signal DQ from the memory device 300. The seventh pinP27 may include a plurality of pins corresponding to a plurality of datainput/output signals DQ.

The controller I/F 410 may transmit the data input/output signal DQincluding the command CMD or the address ADDR to the memory device 300together with the toggling write enable signal nWE. In other words,while the write enable signal nWE is toggled, the data input/outputsignal DQ including the command CMD or the address ADDR may betransmitted to the memory device 300. The controller I/F 410 maytransmit, to the memory device 300, the data input/output signal DQincluding the command CMD to the memory device 300 as the command latchenable signal CLE in an enable state is transmitted, and may transmitthe data input/output signal DQ including the address to the memorydevice 300 as the address latch enable signal ALE is transmitted.

The controller I/F 410 may transmit the read enable signal nRE to thememory device 300 via the fifth pin P25. The controller I/F 410 mayreceive the data strobe signal DQS from the memory device 300 via thesixth pin P26, or may transmit the data strobe signal DQS to the memorydevice 300.

In the data (DATA) output operation of the memory device 300, thecontroller I/F 410 may toggle the read enable signal nRE, and transmitthe read enable signal nRE to the memory device 300. For example, thecontroller I/F 410 may generate the read enable signal nRE that ischanged from a toggle-off state (for example, a high level state or alow level state) to a toggle state before the data DATA is output.Accordingly, the memory device 300 may generate the data strobe signalDQS that toggles in response to the read enable signal nRE. Thecontroller I/F 410 may receive the data input/output signal DQ includingthe data DATA together with the toggling data strobe signal DQS from thememory device 300. In other words, while the data strobe signal DQS istoggled, the controller I/F 410 may receive the data input/output signalDQ including the data DATA from the memory device 300. The controllerI/F 410 may obtain the data DATA from the data input/output signal DQbased on the toggle timing of the data strobe signal DQS.

In the data DATA input operation of the memory device 300, thecontroller I/F 410 may generate the toggling data strobe signal DQS. Forexample, the controller I/F 410 may generate the data strobe signal DQSthat is changed from a toggle-off state (for example, a high level stateor a low level state) to a toggle state before transmitting the dataDATA. The controller I/F 410 may transmit the data input/output signalDQ including the data DATA to the memory device 300 based on the toggletiming of the data strobe signal DQS.

The controller I/F 410 may receive the ready/busy output signal nR/Bfrom the memory device 300 via the eighth pin P28. The controller I/F410 may determine state information of the memory device 300 based onthe ready/busy output signal nR/B.

FIG. 3 illustrates the memory system 20 of FIG. 2 for exchanging datainput/output signals, according to an embodiment of the inventiveconcept. Referring to FIG. 3, the memory device 300 may include a DQ pinDQ_P, a first transmitter (Tx1) 301, and a first receiver (Rx1) 302. TheDQ pin DQ_P may correspond to the seventh pin P17 in FIG. 2. Forexample, when the seventh pin P17 includes a plurality of pins, the DQpin DQ_P may correspond to one of the plurality of pins.

The Tx1 301 may generate the data input/output signal DQ based on thedata DATA, and transmit the data input/output signal DQ to the memorycontroller 400 via the DQ pin DQ_P. In an embodiment of the inventiveconcept, the Tx1 301 may generate the data input/output signal DQ byusing an N-level pulse amplitude modulation (hereinafter, referred to aspulse amplitude modulation (PAM)-N) (N is a natural number of 3 or more)method, or a 2-level PAM (hereinafter, referred to as a non return tozero (NRZ)) method based on the data DATA. For example, the Tx1 301 mayuse one of PAM-4, PAM-8, and PAM-16 methods.

A PAM-N method may be a modulation method for transmitting a pluralityof bits during one unit interval, and the NRZ method may be a modulationmethod for transmitting one bit during one unit interval. In this case,the unit interval may correspond to a symbol period for transmitting onesymbol of the data input/output signal DQ. For example, when the dataDATA is modulated by the PAM-N method, one symbol may include aplurality of data bits. When the data DATA is modulated in the NRZmethod, one symbol may include one data bit.

The Rx1 302 may receive the data input/output signal DQ from the memorycontroller 400 via the DQ pin DQ_P, and obtain the command CMD, theaddress ADDR, or the data DATA from the data input/output signal DQ. Inan embodiment of the inventive concept, the Rx1 302 may sample thereceived data input/output signal DQ in the PAM-N mode or the NRZ mode,and obtain the command CMD, the address ADDR, or the data DATA. Forexample, in the PAM-N mode, the Rx1 302 may output the plurality of bitsbased on the voltage level of the data input/output signal DQ receivedduring one unit interval. In the NRZ mode, the Rx1 302 may output onebit based on the voltage level of the data input/output signal DQreceived during one unit interval.

In an embodiment of the inventive concept, the mode of the Rx1 302 mayvary according to a symbol type of the received data input/output signalDQ. In other words, the mode of the Rx1 302 may vary depending onwhether the command CMD is received via the data input/output signal DQ,the address ADDR is received, or the data DATA is received. For example,when the command CMD and the address ADDR are received, the Rx1 302 mayoperate in the PAM-N mode, and when the data DATA is received, the Rx1302 may operate in the NRZ mode.

The memory controller 400 may include a DQ pin DQ_P′, a secondtransmitter (Tx2) 401, and a second receiver (Rx2) 402. The DQ pin DQ_P′may correspond to the DQ pin DQ_P of the memory device 300. In otherwords, the DQ pin DQ_P′ and the DQ pin DQ_P may be connected to eachother. When the seventh pin P27 includes a plurality of pins, the DQ pinDQ_P′ may correspond to one of the plurality of pins.

The Tx2 401 may generate a data input/output signal DQ based on thecommand CMD, the address ADDR, and the data DATA, and transmit the datainput/output signal DQ to the memory device 300 via the DQ pin DQ_P′. Inan embodiment of the inventive concept, the Tx2 401 may generate thedata input/output signal DQ by the PAM-N method or the NRZ method basedon the command CMD, the address ADDR, and the data DATA. The modulationmethod of the data input/output signal DQ may vary depending on thesymbol type to be included in the data input/output signal DQ. In otherwords, the modulation method may vary depending on whether the commandCMD is transmitted, the address ADDR is transmitted, or the data DATA istransmitted via the data input/output signal DQ. For example, the Tx2401 may transmit the command CMD and the address ADDR by the PAM-Nmethod, and transmit the data DATA by the NRZ method.

The Rx2 402 may receive the data input/output signal DQ from the memorydevice 300 via the DQ pin DQ_P′, and obtain the data DATA from the datainput/output signal DQ. In an embodiment of the inventive concept, theRx2 402 may obtain the data DATA by sampling the received datainput/output signal DQ in the PAM-N mode or the NRZ mode. For example,in the PAM-N mode, the Rx2 402 may output the plurality of data bitsbased on the voltage level of the data input/output signal DQ receivedduring one unit interval. In the NRZ mode, the Rx2 402 may output onedata bit based on the voltage level of the data input/output signal DQreceived during one unit interval.

In an embodiment of the inventive concept, the modulation method of thedata input/output signal DQ may be determined according to a certainconvention. In this case, the modes of the Rx1 302 and the Rx2 402 forsampling the data input/output signal DQ may be determined to correspondto the modulation methods of the Tx1 301 and the Tx2 401 according to acertain convention. In another embodiment of the inventive concept, thememory controller 400 may transmit signaling information about amodulation method of the data input/output signal DQ to the memorydevice 300. The memory device 300 may determine a modulation method ofthe Tx1 301 and a mode of the Rx1 302 based on signaling informationreceived from the memory controller 400.

FIG. 4A is a graph illustrating an example of a data eye for describingthe PAM-4 method of the data input/output signal DQ, according to anembodiment of the inventive concept. FIG. 4B is a graph illustrating anexample of a data eye for describing the NRZ method of the datainput/output signal DQ, according to an embodiment of the inventiveconcept. The horizontal axes of the graphs of FIGS. 4A and 4B may denotetime, and the vertical axes thereof may denote voltage levels.

Referring to FIGS. 3 and 4A, the data input/output signal DQ may betransmitted between the memory device 300 and the memory controller 400by the PAM-4 method. In this case, the data input/output signal DQ maybe generated to have one of first through fourth voltage levels VL1through VL4. Accordingly, two bits (for example, one of ‘11’, ‘10’,‘01’, and ‘00’) during one unit interval UI may be transmitted betweenthe memory device 300 and the memory controller 400 via the datainput/output signal DQ. For example, bits ‘11’ may correspond to thefirst voltage level VL1, bits ‘10’ may correspond to the second voltagelevel VL2, bits ‘01’ may correspond to the third voltage level VL3, andbits ‘00’ may correspond to the fourth voltage level VL4. In otherwords, during the unit interval UI, a symbol having one of the firstthrough fourth voltage levels VL1 through VL4 may be generated, and eachof the symbols may correspond to two bits.

The data input/output signal DQ transmitted by the PAM-4 method may besampled based on first through third reference voltages Vref1 throughVref3. For example, when the voltage level of the data input/outputsignal DQ is greater than the first reference voltage Vref1, the datainput/output signal DQ may be decoded into bits ‘11’. When the voltagelevel of the data input/output signal DQ is less than the firstreference voltage Vref1 and greater than the second reference voltageVref2, the data input/output signal DQ may be decoded into bits ‘10’.When the voltage level of the data input/output signal DQ is less thanthe second reference voltage Vref2 and greater than the third referencevoltage Vref3, the data input/output signal DQ may be decoded into bits‘01’. When the voltage level of the data input/output signal DQ is lessthan the third reference voltage Vref3, the data input/output signal DQmay be decoded into bits ‘00’.

For example, when the memory controller 400 transmits the command CMD tothe memory device 300 by the PAM-4 method, the Tx2 401 may transmit thedata input/output signal DQ having a voltage level corresponding to thetwo bits of the command CMD of the first through fourth voltage levelsVL1 through VL4 to the memory device 300 during one unit interval UI.The Rx1 302 may compare the voltage level of the data input/outputsignal DQ to each of the first through third reference voltages Vref1through Vref3 in the PAM-4 mode, and obtain two bits corresponding tothe data input/output signal DQ. In other words, the Rx1 302 maydetermine the bits corresponding to the data input/output signal DQ.

Referring to FIGS. 3 and 4B, the data input/output signal DQ may betransmitted between the memory device 300 and the memory controller 400by the NRZ method. In this case, the data input/output signal DQ may begenerated to have one of the first and fourth voltage levels VL1 andVL4. The first voltage level VL1 of the NRZ method may correspond to thefirst voltage level VL1 of the PAM-4 method, and the fourth voltagelevel VL4 of the NRZ method may correspond to the fourth voltage levelVL4 of the PAM-4 method. Accordingly, one bit (for example, one of ‘1’and ‘0’) may be transmitted via the data input/output signal DQ duringone unit interval UI between the memory device 300 and the memorycontroller 400. For example, the bit ‘1’ may correspond to the firstvoltage level VL1, and the bit ‘0’ may correspond to the fourth voltagelevel VL4. In other words, during the unit interval UI, a symbol havingone of the first and fourth voltage levels VL1 and VL4 may be generated,and each of the symbols may correspond to one bit.

The data input/output signal DQ transmitted by the NRZ method may besampled based on the second reference voltage Vref2. The secondreference voltage Vref2 of the NRZ method may correspond to the secondreference voltage Vref2 in FIG. 4A. For example, when the voltage levelof the data input/output signal DQ is greater than the second referencevoltage Vref2, the data input/output signal DQ may be decoded into thebit ‘1’. When the voltage level of the data input/output signal DQ isless than the second reference voltage Vref2, the data input/outputsignal DQ may be decoded into the bit ‘0’.

For example, when the memory controller 400 transmits the data DATA tothe memory device 300 by the NRZ method, the Tx2 401 may transmit thedata input/output signal DQ having a voltage level corresponding to onebit of the data DATA of the first and fourth voltage levels VL1 and VL4to the memory device 300 during the unit interval UI. The Rx1 302 mayobtain one bit corresponding to the data input/output signal DQ bycomparing the voltage level of the data input/output signal DQ to thesecond reference voltage Vref2 in the NRZ mode. In other words, the Rx1302 may determine the one bit corresponding to the data input/outputsignal DQ.

In FIG. 4B, a reference voltage for sampling the data input/outputsignal DQ in the NRZ mode is illustrated as the second reference voltageVref2, but the inventive concept is not limited thereto. For example,various voltages (for example, the first reference voltage Vref1 or thethird reference voltage Vref3 in FIG. 4A) may be used as a referencevoltage for sampling the data input/output signal DQ in the NRZ mode.

With respect to FIGS. 4A and 4B, for convenience of description, thePAM-4 method has been described, but the inventive concept is notlimited thereto. For example, when the data input/output signal DQ istransmitted between the memory device 300 and the memory controller 400by the PAM-N method, the data input/output signal DQ may be generated tohave one of the first through N^(th) voltage levels, for example, firstthrough eighth voltage levels. Accordingly, M bits (M is a naturalnumber of 2 or more) may be transmitted between the memory device 300and the memory controller 400 during the unit interval UI via the datainput/output signal DQ. For example, when the data input/output signalDQ is transmitted by a PAM-8 method, 3 bits may be transmitted duringthe unit interval UI, and when the data input/output signal DQ istransmitted by a PAM-16 method, 4 bits may be transmitted during theunit interval UI. In other words, N may be an M power of 2. In thiscase, the data input/output signal DQ transmitted by the PAM-N methodmay be sampled based on the first through (N−1)^(th) reference voltages.

FIGS. 5A through 5D illustrate signaling methods of the datainput/output signal DQ, according to embodiments of the inventiveconcept. The memory device 300 and the memory controller 400 in FIG. 3(for example, the first and second transmitters 301 and 401 and thefirst and second receivers 302 and 402) may generate the datainput/output signal DQ and sample the data input/output signal DQ, basedon the signaling methods illustrated in FIGS. 5A through 5D.

Referring to FIGS. 3 and 5A, the command CMD and the address ADDR may betransmitted by the PAM-N method, and the data DATA may be transmitted bythe NRZ method. For example, the memory controller 400 may transmit thecommand CMD and the address ADDR to the memory device 300 by the PAM-Nmethod, and transmit the data DATA corresponding to the command CMD bythe NRZ method. In this case, the memory device 300 may obtain thecommand CMD and the address ADDR in the PAM-N mode, and obtain the dataDATA in the NRZ mode. In FIG. 5A, the PAM-N mode may occur before theNRZ mode.

Referring to FIGS. 3 and 5B, the command CMD and the address ADDR may betransmitted by the NRZ method, and the data DATA may be transmitted bythe PAM-N method. For example, the memory controller 400 may transmitthe command CMD and the address ADDR to the memory device 300 by the NRZmethod, and transmit the data DATA corresponding to the command CMD bythe PAM-N method. In this case, the memory device 300 may obtain thecommand CMD and the address ADDR in the NRZ mode, and obtain the dataDATA in the PAM-N mode. In FIG. 5B, the NRZ mode may occur before thePAM-N mode.

Referring to FIGS. 3 and 5C, the command CMD, the address ADDR, and thedata DATA may be transmitted by the PAM-N method. For example, thememory controller 400 may transmit the command CMD, the address ADDR,and the data DATA corresponding to the command CMD to the memory device300 by the PAM-N method. In this case, the memory device 300 may obtainthe command CMD, the address ADDR, and the data DATA in the PAM-N mode.

Referring to FIGS. 3 and 5D, the command CMD, the address ADDR, and thedata DATA may be transmitted by the NRZ method. The memory controller400 may transmit the command CMD, the address ADDR, and the data DATAcorresponding to the command CMD to the memory device 300 by the NRZmethod. In this case, the memory device 300 may obtain the command CMD,the address ADDR, and the data DATA in the NRZ mode.

As described above, the memory device 300 and the memory controller 400may exchange the data input/output signal DQ based on the PAM-N and NRZmodes. For example, as illustrated in FIG. 5A, when the datainput/output signal DQ corresponding to at least one of the command CMD,the address ADDR, and the data DATA is transmitted in the PAM-N mode,the data input/output signal DQ corresponding to the rest of the commandCMD, the address ADDR, and the data DATA may be transmitted in the NRZmode. As illustrated in FIG. 5B, when the data input/output signal DQcorresponding to at least one of the command CMD, the address ADDR, andthe data DATA is transmitted in the NRZ mode, the data input/outputsignal DQ corresponding to the rest of the command CMD, the addressADDR, and the data DATA may be transmitted in the PAM-N mode.

According to the modulation method of FIG. 5A, the transmission time ofthe command CMD and the address ADDR may be reduced compared to themodulation method of FIG. 5D. In this case, ratios of the command CMDand the address ADDR transmission time to the data DATA transmissiontime may be reduced. Accordingly, the ratio of the data DATAtransmission time to the total transmission time of the command CMD, theaddress ADDR, and the data DATA may be increased, and the input/outputefficiency of the memory system 20 may be increased. In addition, whenthe command CMD and the address ADDR transmission time is reduced, asillustrated in FIG. 1, the interleave operation time for n memorydevices connected to one channel may be reduced.

According to the modulation methods of FIGS. 5B and 5C, more bits ofdata DATA may be transmitted during a unit time compared to themodulation method of FIG. 5D. Accordingly, the data bandwidth of thememory device 300 may be increased. In addition, the modulation methodof FIG. 5B may increase the transmission time of the command CMD and theaddress ADDR compared to the modulation method of FIG. 5C, but thereliability of the command CMD and the address ADDR provided to thememory device 300 may be increased by the modulation method of FIG. 5B.According to the modulation method of FIG. 5D, the memory device 300 mayexchange the data input/output signal DQ with a memory controller thatdoes not support the PAM-N method. In other words, the memory device 300may be used by a memory controller that supports the PAM-N mode or amemory controller that does not support the PAM-N mode.

Hereinafter, for convenience of description, embodiments of theinventive concept will be described in which the data input/outputsignal DQ is transmitted by one of the PAM-N method and the NRZ methodbased on the embodiment of FIG. 5A, and the memory device 300 and thememory controller 400 perform the sampling of the data input/outputsignal DQ in one of the PAM-N mode and the NRZ mode. However, theinventive concept is not limited thereto, and the following embodimentsmay be applied to the embodiments of FIGS. 5B through 5D.

FIG. 6 is a flowchart of an example operation of the memory device 300in FIG. 3, according to the signaling method of FIG. 5A. Referring toFIGS. 3 and 6, the memory device 300 may receive the command CMD and theaddress ADDR transmitted by the memory controller 400 by the PAM-Nmethod (S301). For example, the memory device 300 may receive thecommand CMD and the address ADDR from the memory controller 400 based onthe data input/output signal DQ having one of N different voltagelevels. In this case, the memory device 300 may obtain the command CMDand the address ADDR corresponding to the voltage level of the datainput/output signal DQ based on the first through (N−1)^(th) referencevoltages in the PAM-N mode.

The memory device 300 may receive the data DATA transmitted by thememory controller 400 by the NRZ method or transmit the data DATA to thememory controller 400 by the NRZ method (S302). For example, the memorydevice 300 may receive data DATA corresponding to the command CMD (forexample, a program command) based on the data input/output signal DQhaving one of two different voltage levels from the memory controller400. Alternatively, the memory device 300 may transmit the data DATAcorresponding to the command CMD (for example, a read command) based onthe data input/output signal DQ having one of two different voltagelevels to the memory controller 400. In this case, the memory device 300may obtain the data DATA corresponding to the voltage level of the datainput/output signal DQ based on one reference voltage in the NRZ mode.

FIG. 7A is an example timing diagram for a program operation, accordingto the embodiment of FIG. 5A. FIG. 7B is an example timing diagram for aread operation, according to the embodiment of FIG. 5A. FIG. 7Aillustrates an example in which the memory device 300 receives thecommand CMD, the address ADDR, and the data DATA from the memorycontroller 400 for the program operation, and FIG. 7B illustrates anexample in which the memory device 300 receives the command CMD and theaddress ADDR from the memory controller 400 for the read operation, andtransmits the data DATA to the memory controller 400.

Referring to FIGS. 7A and 7B, the memory device 300 may receive thewrite enable signal nWE in a toggle state from the memory controller400. The memory device 300 may receive the command CMD and the addressADDR from the memory controller 400 during the interval in which thewrite enable signal nWE is in a toggle state. In other words, the timeperiod in which the command CMD and the address ADDR are received mayoverlap with the time period in which the write enable signal nWEtoggles. The command CMD may be transmitted via the data input/outputsignal DQ during the enable interval of the command latch enable signalCLE (for example, in a high level state), and the address ADDR may betransmitted via the data input/output signal DQ in the enable interval(for example, a high level state) of the address latch enable signalALE. In this case, the memory device 300 may receive the command CMD andthe address ADDR via the data input/output signal DQ transmitted by thePAM-4 method. For example, a program command may be transmitted in theprogram operation, and a read command may be transmitted in the readoperation.

Referring to FIG. 7A, the memory device 300 may receive a data strobesignal DQS in a toggle state from the memory controller 400. The datastrobe DQS may be toggled after the write enable signal nWE is toggled.The memory device 300 may receive data DATA from the memory controller400 in the interval in which the data strobe signal DQS is in a togglestate. In this case, the memory device 300 may receive the data DATA viathe data input/output signal DQ transmitted in the NRZ method.

In the program operation, the memory device 300 may program the dataDATA into the memory cell array 330 in FIG. 2 in response to the programcommand. While a program is being executed, as described with referenceto FIG. 2, the memory device 300 may transmit the ready/busy outputsignal nR/B indicating a busy state (for example, a low level) to thememory controller 400.

Referring to FIG. 7B, the memory device 300 may receive the read enablesignal nRE in a toggle state from the memory controller 400. The readenable signal nRE may be toggled after the write enable signal nWE. Thememory device 300 may transmit the data strobe signal DQS in a togglestate to the memory controller 400 in response to toggling of the readenable signal nRE. In other words, the data strobe signal DQS begins totoggle after the read enable signal RE begins to toggle. For example,the first rising edge of the data strobe signal DQS may occur after atime period tDQSRE from the first rising edge of the read enable signalnRE. For example, the memory device 300 may transmit the data DATA fromthe memory controller 400 in an interval in which the data strobe signalDQS is in a toggle state. In this case, the memory device 300 maytransmit the data DATA to the memory controller 400 via the datainput/output signal DQ generated in the NRZ method.

In the read operation, the memory device 300 may read the data DATA fromthe memory cell array 330 in FIG. 2 in response to the read command.While the read operation is being executed, as described with referenceto FIG. 2, the memory device 300 may transmit the ready/busy outputsignal nR/B indicating a busy state (for example, a low level) to thememory controller 400.

Hereinafter, for convenience of description, embodiments will bedescribed based on an example in which the data input/output signal DQis transmitted by the PAM-4 method, as illustrated in FIGS. 7A and 7B.However, the inventive concept is not limited thereto, and embodimentsof the PAM-4 method may be extended to embodiments of the PAM-N methods(for example, PAM-8 and PAM-16 methods).

FIG. 8 is an example block diagram of the memory device 300 in FIG. 2.Referring to FIG. 8, the memory device 300 includes the memory interfacecircuit 310, the control logic circuit 320, the memory cell array 330, apage buffer circuit 340, a voltage generator 350, and a row decoder 360.The memory device 300 may further include a column logic, a pre-decoder,a temperature sensor, a command decoder, an address decoder, etc.

The memory interface circuit 310 may transmit the command CMD and theaddress ADDR received from the memory controller 400 via the datainput/output signal DQ, and a control signal CTRL received via varioussignals (for example, CLE, ALE, nWE, and nRE, DQS, etc.) to the controllogic circuit 320. The memory interface circuit 310 may transmit thedata DATA received from the memory controller 400 via the datainput/output signal DQ to the page buffer circuit 340. In addition, thememory interface circuit 310 may transmit the data DATA transmitted bythe page buffer circuit 340 to the memory controller 400 via the datainput/output signal DQ.

In an embodiment of the inventive concept, the memory interface circuit310 may operate according to a mode signal MODE from the control logiccircuit 320. For example, the memory interface circuit 310 may samplethe data input/output signal DQ of the PAM-4 mode in the PAM-4 mode orgenerate the data input/output signal DQ in the PAM-4 mode, in responseto the mode signal MODE. The memory interface circuit 310 may sample thedata input/output signal DQ in the NRZ mode or generate the datainput/output signal DQ in the NRZ mode, in response to the mode signalMODE in the NRZ mode.

The control logic circuit 320 may control various operations in thememory device 300. The control logic circuit 320 may output variouscontrol signals in response to the command CMD and/or the address ADDRfrom the memory interface circuit 310. For example, the control logiccircuit 320 may output a voltage control signal CTRL_vol, a row addressX-ADDR, a column address Y-ADDR, and the mode signal MODE.

In an embodiment of the inventive concept, the control logic circuit 320may generate the mode signal MODE based on the control signal CTRL. Thecontrol logic circuit 320 may determine a symbol type of the datainput/output signal DQ received via the memory interface circuit 310based on the control signal CTRL. The control logic circuit 320 maygenerate the mode signal MODE according to the symbol type, as describedwith reference to FIGS. 5A through 5D. For example, the control logiccircuit 320 may determine that the command CMD and the address ADDR arereceived via the data input/output signal DQ based on the control signalCTRL, and may generate the mode signal MODE corresponding to the PAM-4mode. The control logic circuit 320 may determine that the data DATA isreceived via the data input/output signal DQ based on the control signalCTRL, and may generate the mode signal MODE corresponding to the NRZmode.

The memory cell array 330 may include a plurality of memory blocks BLK1through BLKz (z is a positive integer), and each of the plurality ofmemory blocks BLK1 through BLKz may include a plurality of memory cells.The memory cell array 330 may be connected to the page buffer circuit340 via bit lines BL, and may be connected to the row decoder 360 viaword lines WL, string select lines SSL, and ground select lines GSL.

In an embodiment of the inventive concept, the memory cell array 330 mayinclude a three-dimensional memory cell array, and the three-dimensionalmemory cell array may include a plurality of NAND strings. Each NANDstring may include memory cells respectively connected to word linesvertically stacked on a substrate. U.S. Pat. Nos. 7,679,133, 8,553,466,8,654,587, 8,559,235, and U.S. Patent Application Publication No.2011/0233648 are incorporated by reference herein in their entireties.In an embodiment of the inventive concept, the memory cell array 330 mayinclude a two-dimensional memory cell array, and the two-dimensionalmemory cell array may include a plurality of NAND strings that arearranged in rows and columns.

The page buffer circuit 340 may include a plurality of page buffers PB1through PBp (p is an integer of 3 or more), and the plurality of pagebuffers PB1 through PBp may be connected to the memory cells via theplurality of bit lines BL. The page buffer circuit 340 may select atleast one bit line BL of the bit lines BL in response to the columnaddress Y-ADDR. The page buffer circuit 340 may operate as a writedriver or a sense amplifier according to an operation mode. For example,during a program operation, the page buffer circuit 340 may apply a bitline voltage corresponding to data to be programmed to the selected bitline BL. During a read operation, the page buffer circuit 340 may sensedata stored in the memory cell by sensing a current or voltage of theselected bit line.

The voltage generator 350 may generate various types of voltages forperforming program, read, and erase operations based on the voltagecontrol signal CTRL_vol. For example, the voltage generator 350 maygenerate a program voltage, a read voltage, a program verificationvoltage, an erase voltage, or the like, as a word line voltage VWL.

The row decoder 360 may select one of the plurality of word lines WL inresponse to the row address X-ADDR, and may select one of the pluralityof string select lines SSL. For example, during the program operation,the row decoder 360 may apply the program voltage and the programverification voltage to the selected word line WL, and may apply theread voltage to the selected word line WL during the read operation.

FIG. 9 is a diagram of examples for generating the mode signals MODE inFIG. 8. Referring to FIGS. 8 and 9, the control logic circuit 320 maygenerate the mode signals MODE based on various conditions. The datainput/output signal DQ including the command CMD and the address ADDRmay be sampled in the PAM-4 mode and the data input/output signal DQincluding the data DATA may be sampled in the NRZ mode, according to themode signal MODE generated based on the conditions in FIG. 9. Inaddition, the data input/output signal DQ including the data DATA may begenerated in the NRZ method according to the mode signal MODE generatedbased on the conditions in FIG. 9.

In an embodiment of the inventive concept, when the command latch enablesignal CLE or the address latch enable signal ALE is in an enable state,the control logic circuit 320 may generate the mode signal MODEcorresponding to the PAM-4 mode. This is illustrated in CASE 1. When thecommand latch enable signal CLE and the address latch enable signal ALEare disabled, the control logic circuit 320 may generate the mode signalMODE corresponding to the NRZ mode. This is illustrated in CASE 1.

In an embodiment of the inventive concept, the control logic circuit 320may generate the mode signal MODE based on a DQ enable signal DQE. Inthis case, the DQ enable signal DQE may include the control signal CTRLtransmitted by the memory controller 400 by the PAM-4 method, todistinguish the symbol type of the data input/output signal DQ. The DQenable signal DQE may be transmitted by the memory controller 400 to thememory device 300 via a separate pin. In this case, the command latchenable signal CLE and the address latch enable signal ALE may not betransmitted. Accordingly, the number of pins used to distinguish thesymbol type of the data input/output signal DQ may be reduced.

For example, when a voltage level of the DQ enable signal DQE is thefirst voltage level VL1, the command CMD may be transmitted via the datainput/output signal DQ. When the voltage level of the DQ enable signalDQE is the second voltage level VL2, the address ADDR may be transmittedvia the data input/output signal DQ. When the voltage level of the DQenable signal DQE is the third voltage level VL3, the data DATA may betransmitted via the data input/output signal DQ. In other words, thefirst voltage level VL1 of the DQ enable signal DQE may correspond to anenable state of the command latch enable signal CLE, and the secondvoltage level VL2 of the DQ enable signal DQE may correspond to anenable state of the address latch enable signal ALE. Accordingly, whenthe voltage level of the DQ enable signal DQE is the first voltage levelVL1 or the second voltage level VL2, the control logic circuit 320 maygenerate the mode signal MODE corresponding to the PAM-4 mode, and whenthe voltage level of the DQ enable signal DQE is the third voltage levelVL3 or the fourth voltage level VL4, the control logic circuit 320 maygenerate the mode signal MODE corresponding to the NRZ mode. This isillustrated in CASE 2.

In an embodiment of the inventive concept, when the write enable signalnWE is in a toggle state, the control logic circuit 320 may generate themode signal MODE corresponding to the PAM-4 mode. This is illustrated inCASE 3. When the write enable signal nWE is in a toggle-off state (forexample, a high level state), the control logic circuit 320 may generatethe mode signal MODE corresponding to the NRZ mode. This is illustratedin CASE 3.

In an embodiment of the inventive concept, when the data strobe signalDQS received from the memory controller 400 or transmitted to the memorycontroller 400 is in a toggle-off state (for example, a high level stateor a high resistance (hi-z) state), the control logic circuit 320 maygenerate the mode signal MODE corresponding to the PAM-4 mode. This isillustrated in CASE 4. When the data strobe signal DQS or the readenable signal nRE received from the memory controller 400 or transmittedto the memory controller 400 is in a toggle state, the control logiccircuit 320 may generate the mode signal MODE corresponding to the NRZmode. This is illustrated in CASE 4. For example, when the data strobesignal DQS is in a toggle state in the program operation, the controllogic circuit 320 may generate the mode signal MODE corresponding to theNRZ mode. When the data strobe signal DQS or the read enable signal nREis in a toggle state in the read operation, the control logic circuit320 may generate the mode signal MODE corresponding to the NRZ mode.

In an embodiment of the inventive concept, the control logic circuit 320may generate the mode signal MODE based on a mode setting signal MSS. Inthis case, the mode setting signal MSS may be the control signal CTRLtransmitted by the memory controller 400 to the memory device 300 todetermine a sampling method or a modulation method for the datainput/output signal DQ of the memory device 300. The mode setting signalMSS may be transmitted by the memory controller 400 to the memory device300 via a separate mode setting pin (for example, a flag pin). Forexample, when ‘1’ is transmitted via the mode setting signal MSS, thecontrol logic circuit 320 may generate the mode signal MODEcorresponding to the PAM-4 mode. This is illustrated in CASE 5. When ‘0’is transmitted via the mode setting signal MSS, the control logiccircuit 320 may generate the mode signal MODE corresponding to the NRZmode. This is illustrated in CASE 5. However, the inventive concept isnot limited thereto, and the mode signal MODE indicating various modes(for example, PAM-4, PAM-8, PAM-16, and NRZ modes) based on the modesetting signal MSS may be generated. In another embodiment of theinventive concept, the mode setting signal MSS may be transmitted by thememory controller 400 to the memory device 300 based on a set featurecommand.

FIG. 9 illustrates an example in which the control logic circuit 320generates the mode signal MODE according to the embodiment of FIG. 5A,but the examples of generating the mode signals MODE in FIG. 9 may beapplied to the embodiments of FIGS. 5B through 5D. In the embodiment ofFIG. 5B, the control logic circuit 320 may generate the mode signal MODEin modes opposite to the modes of FIG. 9 in response to the conditionsof FIG. 9. For example, when the command latch enable signal CLE or theaddress latch enable signal ALE is in an enable state, the control logiccircuit 320 may generate the mode signal MODE corresponding to the NRZmode. When the command latch enable signal CLE and the address latchenable signal ALE are disabled, the control logic circuit 320 maygenerate the mode signal MODE corresponding to the PAM-4 mode. In thiscase, the data input/output signal DQ including the command CMD and theaddress ADDR may be sampled in the NRZ mode, and the data input/outputsignal DQ including the data DATA may be sampled in the PAM-4 mode. Inaddition, the data input/output signal DQ including the data DATA may begenerated in the PAM-4 method.

Hereinafter, with reference to FIGS. 10 to 16, a transmitter forgenerating the data input/output signal DQ in a method selected from thePAM-4 method and the NRZ method, and a receiver for sampling the datainput/output signal DQ in a mode selected from the PAM-4 mode and theNRZ mode will be described in detail. For convenience of description, atransmitter and a receiver according to embodiments of the inventiveconcept will be described based on the second transmitter 401 and thefirst receiver 302 in FIG. 3. In this case, in FIG. 3, the firsttransmitter 301 and the second receiver 402 may be configuredsubstantially the same as the second transmitter 401 and the firstreceiver 302, respectively.

FIG. 10 is a block diagram of an example of a transmitter, according toan embodiment of the inventive concept. A transmitter 420 may correspondto the second transmitter 401 of the memory controller 400 in FIG. 3.Referring to FIG. 10, the transmitter 420 may include a bit divider or abit splitter 421, a pre-processing circuit 422, a first driver 423, anda second driver 424. The transmitter 420 may further include a resistorRZQ arranged between the DQ pin DQ_P′ and a ground voltage VSS.

The bit splitter 421 may split or divide bits of the command CMD, theaddress ADDR, or the data DATA to be transmitted via the transmitter 420by two bits based on a clock signal CK. The split two bits may bedivided into a most significant bit MSB and a least significant bit LSB.The most significant bit MSB and the least significant bit LSB may beprovided to the pre-processing circuit 422. For example, the mostsignificant bit MSB and the least significant bit LSB may be transmittedto the pre-processing circuit 422 in parallel.

In an embodiment of the inventive concept, a frequency of the clocksignal CK may vary according to the symbol type to be transmitted basedon the data input/output signal DQ. For example, the frequency of theclock signal CK for transmitting the data DATA may be greater than thefrequency of the clock signal CK for transmitting the command CMD andthe address ADDR.

The pre-processing circuit 422 may receive the most significant bit MSBand the least significant bit LSB, and may preprocess the mostsignificant bit MSB and the least significant bit LSB based on the clocksignal CK and a mode switching signal MOS. Accordingly, thepre-processing circuit 422 may generate a first bit BT0 and a second bitBT1. For example, the pre-processing circuit 422 may generate 4-phaseclock signals based on the clock signal CK, and generate the first bitBT0 and the second bit BT1 based on the generated 4-phase clock signals.

The pre-processing circuit 422 may operate in the PAM-4 mode or the NRZmode according to the mode switching signal MOS. For example, thepre-processing circuit 422 may generate the first bit BT0 based on avalue of the least significant bit LSB and may generate the second bitBT1 based on a value of the most significant bit MSB, in response to themode switching signal MOS corresponding to the PAM-4 mode. In this case,the pre-processing circuit 422 may output the first bit BT0 and thesecond bit BT1 respectively corresponding to the least significant bitLSB and the most significant bit MSB at the same timing (for example, anedge timing of the clock signal CK). For example, the pre-processingcircuit 422 may generate the first bit BT0 and the second bit BT1 basedon the value of the most significant bit MSB and then, may generate thefirst bit BT0 and the second bit BT1 based on the value of the leastsignificant bit LSB, in response to the mode switching signal MOSindicating the NRZ mode. Alternatively, the pre-processing circuit 422may generate the first bit BT0 and the second bit BT1 based on the valueof the least significant bit LSB, and then, may generate the first bitBT0 and the second bit BT1 based on the value of the most significantbit MSB. In other words, in the NRZ mode, the first bit BT0 and thesecond bit BT1 may be generated to have the same value according to thevalue of the most significant bit MSB or the least significant bit LSB.In this case, the pre-processing circuit 422 may output the first bitBT0 and the second bit BT1 corresponding to the most significant bit MSBat a first timing (for example, a first edge timing of the clock signalCK), and may output the first bit BT0 and the second bit BT1corresponding to the least significant bit LSB at a second timing (forexample, a second edge timing of the clock signal CK). For example, thepre-processing circuit 422 may generate the first bit BT0 and the secondbit BT1 based on the 4-phase clock signals in the NRZ mode.

The first driver 423 may pull-down or pull-up a voltage of a first nodeN1 based on the second bit BT1. The second driver 424 may pull-down orpull-up the voltage of the first node N1 based on the first bit BT0. Forexample, when the second bit BT1 is ‘0’, the first driver 423 maypull-up the first node N1, and when the second bit BT1 is ‘1’, maypull-down the first node N1. For example, a voltage magnitude of thefirst node N1 changing due to the first driver 423 may be greater thanthat of the first node N1 changing due to the second driver 424.

In the PAM-4 mode, the voltage of the first node N1 may be controlled tobe one of the first through fourth voltage levels VL1 through VL4 inFIG. 4A by the first driver 423 and the second driver 424. In the NRZmode, the voltage of the first node N1 may be controlled to be one ofthe first and fourth voltage levels VL1 and VL4 by the first driver 423and the second driver 424. Accordingly, the data input/output signal DQhaving one of the first through fourth voltage levels VL1 through VL4may be generated in the PAM-4 mode, and the data input/output signal DQhaving one of the first and fourth voltage levels VL1 and VL4 may begenerated in the NRZ mode.

As illustrated in FIG. 10, two drivers, in other words, the first andsecond drivers 423 and 424, may be used to transmit two bits (in otherwords, the most significant bit MSB and the least significant bit LSB)in the PAM-4 mode. However, the inventive concept is not limitedthereto, and M drivers (in other words, first through M^(th) drivers)may be used to transmit M bits in the PAM-N mode. In this case, the bitsplitter 421 may split or divide the bits of the command CMD, theaddress ADDR, and the data DATA by M bits, and the pre-processingcircuit 422 may generate the first through M^(th) bits to be provided toM drivers by pre-processing M bits. Accordingly, the first throughM^(th) drivers may generate a data input/output signal having one of thefirst through M^(th) voltage levels based on the first through M^(th)bits.

FIG. 11A illustrates an example operation of the transmitter 420 of FIG.10 in the PAM-4 mode. FIG. 11B illustrates an example operation of thetransmitter 420 of FIG. 10 in the NRZ mode.

Referring to FIGS. 10 and 11A, in the PAM-4 mode, the transmitter 420may generate the data input/output signal DQ having one of first throughfourth voltage levels VL1 through VL4 based on bits of the command CMD,the address ADDR, or the data DATA. The transmitter 420 may generate thedata input/output signal DQ corresponding to two bits, in other words,the MSB and LSB, during one cycle of the clock signal CK (for example,during the unit interval UI in FIGS. 4A and 4B).

As illustrated in FIG. 11A, when the most significant bit MSB is ‘1’ andthe least significant bit LSB is ‘1’, the pre-processing circuit 422 maygenerate ‘0’ as the first bit BT0, and may generate ‘0’ as the secondbit BT1. In this case, the data input/output signal DQ having the firstvoltage level VL1 may be generated by the first driver 423 and thesecond driver 424.

When the most significant bit MSB is ‘1’ and the least significant bitLSB is ‘0’, the pre-processing circuit 422 may generate ‘1’ as the firstbit BT0 and ‘0’ as the second bit BT1. In this case, the datainput/output signal DQ having the second voltage level VL2 may begenerated by the first driver 423 and the second driver 424.

When the most significant bit MSB is ‘0’ and the least significant bitLSB is ‘1’, the pre-processing circuit 422 may generate ‘0’ as the firstbit BT0 and ‘1’ as the second bit BT1. In this case, the datainput/output signal DQ having the third voltage level VL3 may begenerated by the first driver 423 and the second driver 424.

When the most significant bit MSB is ‘0’ and the least significant bitLSB is ‘0’, the pre-processing circuit 422 may generate ‘1’ as the firstbit BT0 and ‘1’ as the second bit BT1. In this case, the datainput/output signal DQ having the fourth voltage level VL4 may begenerated by the first driver 423 and the second driver 424.

Referring to FIGS. 10 and 11B, in the NRZ mode, the transmitter 420 maygenerate the data input/output signal DQ having one of first and fourthvoltage levels VL1 and VL4 based on bits of the command CMD, the addressADDR, or the data DATA. The transmitter 420 may generate the datainput/output signal DQ corresponding to one bit (for example, the mostsignificant bit MSB) during a first cycle of the clock signal CK(hereinafter, referred to as the first cycle), and may generate the datainput/output signal DQ corresponding to one bit (for example, the leastsignificant bit LSB) during a second cycle of the clock signal CK(hereinafter, referred to as the second cycle).

As illustrated in FIG. 11B, when the most significant bit MSB is ‘1’ andthe least significant bit LSB is ‘1’, the pre-processing circuit 422 maygenerate ‘0’ as the first bit BT0, and generate ‘0’ as the second bitBT1 during the first cycle. In this case, the data input/output signalDQ having the first voltage level VL1 may be generated by the firstdriver 423 and the second driver 424. In other words, in the firstcycle, the data input/output signal DQ may have the first voltage levelVL1. The pre-processing circuit 422 may generate ‘0’ as the first bitBT0 and generate ‘0’ as the second bit BT1 during the second cycle. Inthis case, the data input/output signal DQ having the first voltagelevel VL1 may be generated by the first driver 423 and the second driver424. In other words, in the second cycle, the data input/output signalDQ may have the first voltage level VL1.

When the most significant bit MSB is ‘1’ and the least significant bitLSB is ‘0’, the pre-processing circuit 422 may generate ‘0’ as the firstbit BT0 and ‘0’ as the second bit BT1 during the first cycle. In thiscase, the data input/output signal DQ having the first voltage level VL1may be generated by the first driver 423 and the second driver 424. Inother words, in the first cycle, the data input/output signal DQ mayhave the first voltage level VL1. The pre-processing circuit 422 maygenerate ‘1’ as the first bit BT0 and generate ‘1’ as the second bit BT1during the second cycle. In this case, the data input/output signal DQhaving the fourth voltage level VL4 may be generated by the first driver423 and the second driver 424. In other words, in the second cycle, thedata input/output signal DQ may have the fourth voltage level VL4.

When the most significant bit MSB is ‘0’ and the 1 cast significant bitLSB is ‘1’, the pre-processing circuit 422 may generate ‘1’ as the firstbit BT0 and ‘1’ as the second bit BT1 during the first cycle. In thiscase, the data input/output signal DQ having the fourth voltage levelVL4 may be generated by the first driver 423 and the second driver 424.In other words, in the first cycle, the data input/output signal DQ mayhave the fourth voltage level VL4. The pre-processing circuit 422 maygenerate ‘0’ as the first bit BT0 and generate ‘0’ as the second bit BT1during the second cycle. In this case, the data input/output signal DQhaving the first voltage level VL1 may be generated by the first driver423 and the second driver 424. In other words, in the second cycle, thedata input/output signal DQ may have the first voltage level VL1.

When the most significant bit MSB is ‘0’ and the least significant bitLSB is ‘0’, the pre-processing circuit 422 may generate ‘1’ as the firstbit BT0 and ‘1’ as the second bit BT1 during the first cycle. In thiscase, the data input/output signal DQ having the fourth voltage levelVL4 may be generated by the first driver 423 and the second driver 424.In other words, in the first cycle, the data input/output signal DQ mayhave the fourth voltage level VL4. The pre-processing circuit 422 maygenerate ‘1’ as the first bit BT0 and generate ‘1’ as the second bit BT1during the second cycle. In this case, the data input/output signal DQhaving the fourth voltage level VL4 may be generated by the first driver423 and the second driver 424. In other words, in the second cycle, thedata input/output signal DQ may have the fourth voltage level VL4.

As described above, the most significant bit MSB and the leastsignificant bit LSB (in other words, two bits) may be transmitted duringone cycle of the clock signal CK in the PAM-4 mode, and during twocycles of the clock signal CK in the NRZ mode. Accordingly, the commandCMD and the address ADDR may be transmitted faster in the PAM-4 modethan in the NRZ mode.

FIG. 12 is an example circuit diagram of the first driver 423 and thesecond driver 424 in FIG. 10. Referring to FIG. 12, the first driver 423may include first to fourth p-type transistors (hereinafter, referred toas p-channel metal-oxide-semiconductors (PMOS)) PM1 through PM4 andfirst through fourth n-type transistors (hereinafter, referred to asn-channel metal-oxide-semiconductors (NMOS)) NM1 through NM4. When thesecond bit BT1 is ‘0’, the first through fourth PMOSs PM1 through PM4may be turned on and the voltage of the first node N1 is pulled up basedon the power voltage VDD. In this case, the first through fourth NMOSsNM1 through NM4 may be turned off. When the second bit BT2 is ‘1’, thefirst through fourth NMOSs NM1 through NM4 may be turned on and thevoltage of the first node N1 is pulled down based on the ground voltageVSS. In this case, the first through fourth PMOSs PM1 through PM4 may beturned off.

The second driver 424 may include fifth and sixth PMOSs PM5 and PM6, andfifth and sixth NMOSs NM5 and NM6. When the first bit BT0 is ‘0’, thefifth and sixth PMOSs PM5 and PM6 may be turned on and the voltage ofthe first node N1 may be pulled up based on the power voltage VDD. Inthis case, the fifth and sixth NMOSs NM5 and NM6 may be turned off. Whenthe first bit BT0 is ‘1’, the fifth and sixth NMOSs NM5 and NM6 may beturned on and the voltage of the first node N1 may be pulled down basedon the ground voltage VSS. In this case, the fifth and sixth PMOSs PM5and PM6 may be turned off.

As illustrated in FIG. 12, because the first driver 423 includes moretransistors for pull-up and pull-down operations than the second driver424, a pull-up level and pull-down level of the first node N1 due to thefirst driver 423 may be greater than a pull-up level and pull-down levelof the first node N1 due to the second driver 424. Accordingly,according to the first bit BT0 and the second bit BT1 generated in thePAM-4 mode, the voltage of the first node N1 may be one of the firstthrough fourth voltage levels VL1 through VL4 and the data input/outputsignal DQ having one of the first through fourth voltage levels VL1through VL4 may be generated. In addition, according to the first bitBT0 and the second bit BT1 generated in the NRZ mode, the voltage of thefirst node N1 may have one of the first and fourth voltage levels VL1and VL4 and the data input/output signal DQ having one of the first andfourth voltage levels VL1 and VL4 may be generated.

FIG. 13 is a block diagram of an example of a receiver, according to anembodiment of the inventive concept. A receiver 370 may correspond tothe first receiver 302 in the memory device 300 in FIG. 3. Referring toFIG. 13, the receiver 370 may include first through third senseamplifiers 371 through 373, an output decoder 374, and a registercircuit 375.

Each of the first through third sense amplifiers 371 through 373 mayreceive the data input/output signal DQ. Each of the first through thirdsense amplifiers 371 through 373 may operate based on a first internalclock signal ICK1. The first sense amplifier 371 may compare the voltagelevel of the data input/output signal DQ to the first reference voltageVref1 and output a first comparison result DT1. The second senseamplifier 372 may compare the voltage level of the data input/outputsignal DQ to the second reference voltage Vref2 and output a secondcomparison result DT2. The third sense amplifier 373 may compare thevoltage level of the data input/output signal DQ to the third referencevoltage Vref3 and output a third comparison result DT3. For example,when the voltage level of the data input/output signal DQ is greaterthan the first reference voltage Vref1, the first sense amplifier 371may output ‘1’ as the first comparison result DT1. When the voltagelevel of the data input/output signal DQ is less than the firstreference voltage Vref1, the first sense amplifier 371 may output ‘0’ asthe first comparison result DT1. As another example, when the voltagelevel of the data input/output signal DQ is greater than the thirdreference voltage Vref3, the third sense amplifier 373 may output ‘1’ asthe third comparison result DT3.

The first through third sense amplifiers 371 through 373 may outputfirst through third comparison results DT1 through DT3 based on thefirst through third comparison enable signals EN1 through EN3,respectively. For example, the first sense amplifier 371 may compare thevoltage level of the data input/output signal DQ to the first referencevoltage Vref1 in response to the first comparison enable signal EN1 inan enable state (for example, a high level state), and output the firstcomparison result DT1. The first sense amplifier 371 may output acertain value (for example, ‘0’) as the first comparison result DT1 inresponse to the first comparison enable signal EN1 in a disabled state(for example, a low level state). In other words, the first comparisonenable signal EN1 controls a comparison operation of the first senseamplifier 371 at a first level and controls an output operation of thefirst sense amplifier 371 at a second level different from the firstlevel. Similarly, the second and third sense amplifiers 372 and 373 mayoutput second and third comparison results DT2 and DT3 based on thesecond and third comparison enable signals EN2 and EN3, respectively.

In an embodiment of the inventive concept, the first through thirdcomparison enable signals EN1 through EN3 may be generated according tothe mode signal MODE in FIG. 8. For example, the first through thirdcomparison enable signals EN1 through EN3 in an enable state may begenerated according to the mode signal MODE corresponding to the PAM-4mode. In this case, the first through third sense amplifiers 371 through373 may compare the voltage level of the data input/output signal DQ tothe first through third reference voltages Vref1 through Vref3, andoutput the first through third comparison results DT1 through DT3.According to the mode signal MODE corresponding to the NRZ mode, thefirst and third comparison enable signals EN1 and EN3 in a disabledstate may be generated and the second comparison enable signal EN2 in anenabled state may be generated. In this case, the first and third senseamplifiers 371 and 373 may output the first and third comparison resultsDT1 and DT3 of a certain value (for example, ‘0’), and the second senseamplifier 372 may compare the voltage level of the data input/outputsignal DQ to the second reference voltage Vref2 and output the secondcomparison result DT2. For example, the first through third comparisonenable signals EN1 through EN3 may be generated by the receiver 370based on the mode signal MODE, or may be provided to the receiver 370together with the mode signal MODE by the control logic circuit 320.

As described with reference to FIG. 2, the first internal clock signalICK1 may be generated based on a signal of a toggle state received fromthe memory controller 400 (for example, the write enable signal nWE orthe data strobe signal DQS). For example, when the write enable signalnWE in a toggle state is received as the command CMD and the addressADDR are received from the memory controller 400, the first internalclock signal ICK1 may be generated based on the write enable signal nWE.When the data strobe signal DQS in a toggle state is received as thedata DATA is received from the memory controller 400, the first internalclock signal ICK1 may be generated based on the data strobe signal DQS.For example, the first internal clock signal ICK1 corresponding to afirst frequency may be generated based on the write enable signal nWE,and the first internal clock signal ICK1 corresponding to a secondfrequency greater than the first frequency may be generated based on thedata strobe signal DQS. Accordingly, a sampling period of the datainput/output signal DQ including the command CMD and the address ADDRmay be greater than a sampling period of the data input/output signal DQincluding the data DATA.

The output decoder 374 may generate a most significant bit MSB′ and aleast significant bit LSB′ by performing the decoding operation based onthe first through third comparison results DT1 through DT3. For example,the output decoder 374 may generate the most significant bit MSB′ andthe least significant bit LSB′ according to a certain decoding rule (forexample, a pre-stored table of FIG. 14). For example, in the PAM-4 mode,both the most significant bit MSB′ and the least significant bit LSB′generated based on the first through third comparison results DT1through DT3 may have valid values. In the NRZ mode, the most significantbit MSB′ generated based on the first through third comparison resultsDT1 through DT3 may have a valid value, while the least significant bitLSB′ has an invalid value. In other words, two bits that are valid maybe output in parallel as the most significant bit MSB′ and the leastsignificant bit LSB′ in the PAM-4 mode, and one of the two valid bitsmay be output as the most significant bit MSB′ at the first timing andthe other one may be output as the most significant bit MSB′ at a secondtiming, in the NRZ mode.

The register circuit 375 may operate based on a second internal clocksignal ICK2 and the mode signal MODE. The register circuit 375 may storethe most significant bit MSB′ and the least significant bit LSB′ ininternal registers based on the second internal clock signal ICK2, andmay output at least one of the most significant bit MSB′ and the leastsignificant bit LSB′ according to the mode signal MODE as the commandCMD, the address ADDR, or the data DATA.

In the PAM-4 mode (in other words, when the mode signal MODEcorresponding to the PAM-4 mode is received), the register circuit 375may output the most significant bit MSB′ and the least significant bitLSB′ that are stored based on the second internal clock signal ICK2. Forexample, the register circuit 375 may output the most significant bitMSB′ and the least significant bit LSB′ in series or in parallel. In theNRZ mode (in other words, when the mode signal MODE corresponding to theNRZ mode is received), the register circuit 375 may output only the mostsignificant bit MSB′ among the most significant bit MSB′ and the leastsignificant bit LSB′ that are stored based on the second internal clocksignal ICK2. In the PAM-4 mode and the NRZ mode, bits output from theregister circuit 375 may be transmitted to a core circuit (for example,the control logic circuit 320 or the page buffer circuit 340 in FIG. 8)as the command CMD, the address ADDR, or the data DATA.

The second internal clock signal ICK2 may be generated based on a signalin a toggle state received from the memory controller 400. For example,the second internal clock signal ICK2, like the first internal clocksignal ICK1, may be generated based on the write enable signal nWE orthe data strobe signal DQS. For example, the second internal clocksignal ICK2 may include a plurality of clock signals having differentphases from each other (for example, clock signals ICK2[0] and ICK2[1]in FIG. 15A). In this case, the most significant bit MSB′ and the leastsignificant bit LSB′ may be stored in the register circuit 375 based onthe plurality of clock signals.

As illustrated in FIG. 13, in the PAM-4 mode, three sense amplifiers, inother words, 371 through 373, may be used to obtain two bits (forexample, the most significant bit MSB′ and least significant bit LSB′)from the data input/output signal DQ. However, the inventive concept isnot limited thereto, and in the PAM-N mode, (N−1) sense amplifiers (forexample, first through (N−1)^(th) sense amplifiers) may be used toobtain M bits from the data input/output signal DQ. In this case, in thePAM-N mode, the first through (N−1)^(th) sense amplifiers may outputfirst through (N−1)^(th) comparison results by comparing the voltagelevel of the data input/output signal DQ to each of first through(N−1)^(th) reference voltages, and in the NRZ mode, may output the firstthrough (N−1)^(th) comparison results by comparing the voltage level ofthe data input/output signal DQ to a certain reference voltage of thefirst through (N−1)^(th) reference voltages (for example, a referencevoltage of an intermediate level). In the NRZ mode, the first through(N−1)^(th) sense amplifiers may output each of remaining comparisonresults except comparison results corresponding to particular referencevoltages among the first through (N−1)^(th) comparison results as acertain value (for example, ‘0’). The output decoder 374 may output Mbits by performing the decoding operation based on (N−1) comparisonresults. The register circuit 375 may output M bits, that are output bythe output decoder 374 in the PAM-N mode, as the command CMD, theaddress ADDR, or the data DATA, and may output one bit of M bits, thatare output by the output decoder 374 in the NRZ mode, as the commandCMD, the address ADDR, or the data DATA.

FIG. 14 is a diagram of an example operation of the receiver 370 of FIG.13. Referring to FIGS. 13 and 14, when the data input/output signal DQis transmitted by the PAM-4 method, the first through third senseamplifiers 371 through 373 may output ‘111’, ‘011’, ‘001’, and ‘000’, inresponse to the first through fourth voltage levels VL1 through VL4 ofthe data input/output signal DQ, as the first through third comparisonresults DT1 through DT3, respectively. In this case, the output decoder374 may output ‘11’, ‘10’, ‘01’, and ‘00’ as the most significant bitMSB′ and the least significant bit LSB′ in response to the first throughthird comparison results DT1 through DT3. The register circuit 375 mayoutput the output bits ‘11’, ‘10’, ‘01’, and ‘00’, as the command CMD,the address ADDR, or the data DATA. The output bits ‘11’, ‘10’, ‘01’,and ‘00’ may be the same as the most significant bit MSB and the leastsignificant bit LSB corresponding to the first through fourth voltagelevels VL1 through VL4 in FIG. 11A, respectively. In other words, themost significant bit MSB and the least significant bit LSB transmittedby the PAM-4 method by the transmitter 420 of FIG. 10 may be obtained bythe receiver 370 operating in the PAM-4 mode.

When the data input/output signal DQ is transmitted in the NRZ method,the first through third sense amplifiers 371 through 373 may output‘010’ and ‘000’, in response to the first and fourth voltage levels VL1and VL4 of the data input/output signal DQ, as the first through thirdcomparison results DT1 through DT3, respectively. In this case, theoutput decoder 374 may output ‘11’ and ‘00’ as the most significant bitMSB′ and the least significant bit LSB′ in response to the first throughthird comparison results DT1 through DT3. The register circuit 375 mayoutput only the most significant bits MSB′, in other words, ‘1’ and ‘0’among the output bits, in other words, ‘11’ and ‘00’, as the commandCMD, the address ADDR, or the data DATA. The most significant bit MSB′,in other words, ‘1’ and ‘0’ among the output bits, in other words, ‘11’and ‘00’, may be the same as the most significant bit MSB or the leastsignificant bit LSB corresponding to each of the first and fourthvoltage levels VL1 and VL4) in FIG. 11B. For example, when the mostsignificant bit MSB is transmitted during the first cycle in the NRZmethod by the transmitter 420 of FIG. 10, and the least significant bitLSB is transmitted during the second cycle, the most significant bitMSB′ output based on the data input/output signal DQ of the first cyclemay be the same as the most significant bit. MSB, and the mostsignificant bit MSB′ output based on the data input/output signal DQ ofthe second cycle may be the same as the least significant bit LSB. Inother words, the most significant bit MSB and the least significant bitLSB transmitted by the NRZ method by the transmitter 420 of FIG. 10 maybe obtained by the receiver 370 operating in the NRZ mode.

FIG. 15A is a timing diagram of an example operation of the registercircuit 375 in FIG. 13 in the PAM-4 mode. FIG. 15B is a timing diagramof an example operation of the register circuit 375 in FIG. 13 in theNRZ mode. Examples, in which, in the PAM-4 mode and NRZ mode, firstthrough eighth bits B1 through B8 of the command CMD, the address ADDR,or the data DATA are stored in the register circuit 375 based on secondinternal clock signals ICK2[0] and ICK2[1], are described with referenceto FIGS. 15A and 15B. The second internal clock signals ICK2[0] andICK2[1] may have different phases from each other.

Referring to FIG. 15A, in the PAM-4 mode, the register circuit 375 mayreceive the most significant bit MSB′ and the least significant bit LSB′having valid values. For example, at first through fourth time points t1through t4, the register circuit 375 may receive bits B1, B3, B5, and B7as the most significant bit MSB′, respectively, and bits B2, B4, B6, andB8 as the least significant bit LSB′, respectively. The register circuit375 may store the first and second bits B1 and B2 at the first timepoint t1 based on the second internal clock signal ICK2[0] having afirst phase, and may store the fifth and sixth bits B5 and B6 at thetime point t3. For example, when the second internal clock signalICK2[0] is high at the time point t1, the first and second bits B1 andB2 may be stored by the register circuit 375, and when the secondinternal clock signal ICK2[0] is high at the time point t3, the fifthand sixth bits may be stored by the register circuit 375. The registercircuit 375 may store the third and fourth bits B3 and B4 at the secondtime point t2 based on the second internal clock signal ICK2[1] having asecond phase, and may store the seventh and eighth bits B7 and B8 at thetime point t4. The register circuit 375 may output the most significantbit MSB′ and the least significant bit LSB′ stored at each time point asthe command CMD, the address ADDR, or the data DATA.

Referring to FIG. 15B, in the NRZ mode, the register circuit 375 mayreceive the most significant bit MSB′ having a valid value and the leastsignificant bit LSB′ having an invalid value. For example, the registercircuit 375 may receive the first through eighth bits B1 through B8 atthe first through eighth time points t1 through t8, respectively, basedon the most significant bit MSB′. The register circuit 375 may store thefirst, third, fifth, and seventh bits B1, B3, B5, and B7 at the first,third, fifth, and seventh time points t1, t3, t5, and t7, respectively,based on the second internal clock signal ICK2[0] having the firstphase. In other words, the register circuit 375 may store the first,third, fifth, and seventh bits B1, B3, B5, and B7 at the first, third,fifth, and seventh time points t1, t3, t5, and t7, respectively, whenthe second internal clock signal ICK2[0] has a high level. The registercircuit 375 may store the second, fourth, sixth, and eighth bits B2, B4,B6, and B8 at the second, fourth, sixth, and eighth time points t2, t4,t6, and t8, respectively, based on the second internal clock signalICK2[1] having the second phase. In other words, the register circuit375 may store the second, fourth, sixth, and eighth bits B2, B4, B6, andB8 at the second, fourth, sixth, and eighth time points t2, t4, t6, andt8, respectively, when the second internal clock signal ICK2[1] has thehigh level. The register circuit 375 may output only the mostsignificant bit MSB′ stored at each time point as the command CMD, theaddress ADDR, or the data DATA.

In FIGS. 15A and 15B, an example in which the register circuit 375operates based on two second internal clock signals, in other words,ICK2[0] and ICK2[1], is described, but the number of the second internalclock signal ICK2 may be variously changed. For example, the number ofsecond internal clock signals ICK2 may vary according to the number ofinternal registers of the register circuit 375.

FIG. 16 is an example block diagram of the register circuit 375 in FIG.13. The register circuit 375 for performing the operation examples ofFIGS. 15A and 15B may be described with reference to FIG. 16. Theregister circuit 375 may include a first register 381, a second register382, and a select circuit 383.

The first register 381 may store the most significant bit MSB′ based onthe second internal clock signal ICK2[0]. For example, as described withreference to FIGS. 15A and 15B, the first register 381 may store themost significant bit MSB′ having a valid value in the PAM-4 mode and theNRZ mode.

The second register 382 may store the least significant bit LSB′ basedon the second internal clock signal ICK2[1]. For example, as describedwith reference to FIGS. 15A and 15B, the second register 382 may storethe least significant bit LSB′ having a valid value in the PAM-4 mode,and may store the least significant bit LSB′ having an invalid value inthe NRZ mode.

The select circuit 383 may receive the most significant bit MSB′ and theleast significant bit LSB′ stored in the first register 381 and thesecond register 382. The select circuit 383 may output bitscorresponding to the command CMD, the address ADDR, or the data DATAbased on the most significant bit MSB′ and the least significant bitLSB′ according to the mode signal MODE. For example, the select circuit383 may output both the most significant bit MSB′ and the leastsignificant bit LSB′ in the PAM-4 mode, and output only the mostsignificant bit MSB′ in the NRZ mode.

As described above, when the command CMD and the address ADDR arereceived in the PAM-4 method, the select circuit 383 may output the mostsignificant bit MSB′ and the least significant bit LSB′ as the commandCMD and the address, respectively. When the data DATA is received in theNRZ method, the select circuit 383 may output only the most significantbit MSB′ as the data DATA.

FIG. 17 is a block diagram of a solid state drive (SSD) system to whicha memory device is applied, according to an embodiment of the inventiveconcept. Referring to FIG. 17, a SSD system 1000 may include a host 1100and an SSD 1200.

The SSD 1200 may exchange a signal SIG with the host 1100 via a signalconnector 1201, and receive power PWR via a power connector 1202. TheSSD 1200 may include an SSD controller 1210, a plurality of flashmemories (NVMs) 1221 through 122 m, an auxiliary power supply 1230, anda buffer memory 1240. Each of the plurality of NVMs 1221 through 122 mmay be connected to the SSD controller 1210 via a plurality of channels.

The SSD controller 1210 may control the plurality of NVMs 1221 through122 m in response to the signal SIG received from the host 1100. The SSDcontroller 1210 may store a signal generated internally or transmittedfrom the outside (for example, the signal SIG received from the host1100) in the buffer memory 1240. The SSD controller 1210 may correspondto the memory controllers 200 and 400 described above with reference toFIGS. 1 through 16. For example, the SSD controller 1210 may transmitthe command CMD and the address ADDR to the plurality of NVMs 1221through 122 m in the PAM-4 method, and may transmit the data DATA to theplurality of NVMs 1221 through 122 m in the NRZ method. Accordingly, theinput/output efficiency of the SSD 1200 may be increased.

The plurality of NVMs 1221 through 122 m may operate under the controlof the SSD controller 1210. The auxiliary power supply 1230 may beconnected to the host 1100 via the power connector 1202. Each of theplurality of NVMs 1221 through 122 m may correspond to the memorydevices 100 and 200 described above with reference to FIGS. 1 through16. For example, each of the plurality of flash memories 1221 through122 m may sample the command CMD and the address ADDR in the PAM-4 mode,and sample the data DATA in the NRZ mode.

The auxiliary power supply 1230 may be connected to the host 1100 viathe power connector 1202. The auxiliary power supply 1230 may receivepower PWR from the host 1100, and charge the received power PWR. Theauxiliary power supply 1230 may provide power of the SSD 1200 when powersupply from the host 1100 is not smooth.

FIG. 18 is a block diagram of a network system to which a memory systemis applied, according to an embodiment of the inventive concept.Referring to FIG. 18, a network system 2000 may be a facility in whichvarious data is collected and services are provided, and may be referredto as a data center or a data storage center. The network system 2000may include application servers 2100 through 2100 n and storage servers2200 through 2200 m, and the application servers 2100 through 2100 n andthe storage servers 2200 through 2200 m may be referred to as computingnodes. The number of application servers 2100 through 2100 n and thenumber of storage servers 2200 through 2200 m may be variously selectedaccording to embodiments of the inventive concept, and the number ofapplication servers 2100 through 2100 n and the number of storageservers 2200 through 2200 m may be different from each other.

The application servers 2100 through 2100 n and the storage servers 2200through 2200 m may communicate with each other via a network 2300. Thenetwork 2300 may be implemented by using fiber channel (FC), Ethernet,or the like. In this case, the FC may be a medium used for high speeddata transfer, and may use an optical switch providing highperformance/high availability. According to an access method of thenetwork 2300, the storage servers 2200 through 2200 m may be provided asfile storages, block storages, or object storages.

In an embodiment of the inventive concept, the network 2300 may includea storage-dedicated network such as a storage area network (SAN). Forexample, the SAN may include a FC-SAN that is implemented according toFC protocol (FCP) by using an FC network. In an embodiment of theinventive concept, the SAN may include an internet protocol (IP) SAN(IP-SAN) that is implemented according to an Internet (i) small computersystem interface (SCSI) (iSCSI), that is SCSI over transmission controlprotocol/Internet protocol (TCP/IP) or Internet SCSI protocol, by usinga TCP/IP network. In an embodiment of the inventive concept, the network2300 may include a general network such as the TCP/IP network. Forexample, the network 2300 may be implemented according to a protocolsuch as FC over Ethernet (FCoE), a network-attached storage (NAS), and anode version manager (NVM) express (NVMe) over fabrics (oF) (NVMe-oF).

Hereinafter, the application server 2100 and the storage server 2200 aremainly described. Descriptions of the application server 2100 may beapplied to other application servers, e.g., 2100 n, and descriptions ofthe storage server 2200 may be applied to other storage servers, e.g.,2200 m.

The application server 2100 may include a processor 2110 and a memory2120. The processor 2110 may control all operations of the applicationserver 2100, and may access the memory 2120 to execute commands and/ordata loaded in the memory 2120. According to an embodiment of theinventive concept, the number of processors 2110 and the number ofmemories 2120 included in the application server 2100 may be variouslyselected. In an embodiment of the inventive concept, the processor 2110and the memory 2120 may provide a processor-memory pair. In anembodiment of the inventive concept, the number of processors 2110 andthe number of memories 2120 may be different from each other.

The application server 2100 may further include a storage device 2150.The number of storage devices 2150 included in the application server2100 may be variously selected, according to embodiments of theinventive concept. The processor 2110 may provide a command to thestorage device 2150, and the storage device 2150 may operate in responseto a command received from the processor 2110. However, the inventiveconcept is not limited thereto, and the application server 2100 may notinclude the storage device 2150.

The application server 2100 may further include a switch 2130 and anetwork interface card (NIC) 2140. The switch 2130 may selectivelyconnect the processor 2110 to the storage device 2150 under the controlof the processor 2110, or may selectively connect the NIC 2140 to thestorage device 2150. The NIC 2140 may include a wired interface, awireless interface, a Bluetooth interface, an optical interface, or thelike. In an embodiment of the inventive concept, the processor 2110 andthe NIC 2140 may be integrated into one body. In an embodiment of theinventive concept, the storage device 2150 and the NIC 2140 may beintegrated into one body.

The application server 2100 may store data requested by the user orclient to be stored in one of the storage servers 2200 through 2200 mvia the network 2300. In addition, the application server 2100 mayobtain data requested by the user or client to be read from one of thestorage servers 2200 through 2200 m via the network 2300. For example,the application server 2100 may be implemented as a web server, adatabase management system (DBMS), or the like.

The application server 2100 may access the memory 2120 n or the storagedevice 2150 n included in another application server 2100 n via thenetwork 2300, or may access memories 2220 and 2220 m or storage devices2250 and 2250 m included in the storage servers 2200 and 2220 m via thenetwork 2300, respectively. Accordingly, the application server 2100 mayperform various operations on data stored in the application servers2100 and 2100 n and/or the storage servers 2200 and 2200 m. For example,the application server 2100 may execute a command for moving or copyingdata between the application servers 2100 and 2100 n and/or the storageservers 2200 and 2200 m. In this case, data may be moved in an encryptedstate for security or privacy via the network 2300.

The storage server 2200 may include a processor 2210 and a memory 2220.The processor 2210 may control all operations of the storage server2200, and access the memory 2220 to execute commands and/or data loadedin the memory 2220. According to an embodiment of the inventive concept,the number of processors 2210 and the number of memories 2220 includedin the storage server 2200 may be variously selected. In an embodimentof the inventive concept, the processor 2210 and the memory 2220 may beconfigured as a processor-memory pair. In an embodiment of the inventiveconcept, the number of processors 2210 and the number of memories 2220may be different from each other.

The processor 2210 may include a single-core processor or a multi-coreprocessor. For example, the processor 2210 may include a general-purposeprocessor, a central processing unit (CPU), a graphic processing unit(GPU), a digital signal processor (DSP), a microcontroller (MCU), amicroprocessor, a network processor, an embedded processor, a fieldprogrammable gate array (FPGA), an application-specific instruction setprocessor (ASIP), and an application-specific integrated circuitprocessor (ASIC), etc.

The storage server 2200 may further include at least one storage device2250. The number of storage devices 2250 included in the storage server2200 may be variously selected, according to embodiments of theinventive concept. The storage device 2250 may include a controller(CTRL) 2251, a NAND flash memory (NAND) 2252, a DRAM 2253, and aninterface (I/F) 2254. Hereinafter, the configuration and operation ofthe storage device 2250 are described in detail. The followingdescription of the storage device 2250 may be applied to other storagedevices 2150, 2150 n, and 2250 m.

The I/F 2254 may provide a physical connection of the processor 2210 tothe CTRL 2251, and a physical connection of NIC 2240 to the CTRL 2251.For example, the I/F 2254 may be implemented in a direct attachedstorage (DAS) method of directly connecting the storage device 2250 to adedicated cable. In addition, for example, the I/F 2254 may beimplemented in various interface methods such as advanced technologyattachment (ATA), serial ATA (SATA), external SATA (e-SATA), smallcomputer system interface (SCSI), serial attached SCSI (SAS), peripheralcomponent interconnect (PCI), PCI express (PCIe), node version manager(NVM) express (NVMe), IEEE 1394, universal serial bus (USB), a securedigital (SD) card, a multi-media card (MMC), an embedded multi-mediacard (eMMC), and a compact flash (CF) card.

The CTRL 2251 may control all operations of the storage device 2250. TheCTRL 2251 may program data to the NAND 2252 in response to a programcommand, or may read data from the NAND 2252 in response to a readcommand. For example, the program command and/or the read command may beprovided from the processor 2210 in the storage server 2200, theprocessor 2210 m in another storage server 2200 m, or the processors2110 through 2110 n in the application servers 2100 through 2100 n,respectively, via the processor 2210, or directly.

The NAND 2252 may include a plurality of NAND flash memory cells.However, the inventive concept is not limited thereto, and the storagedevice 2250 may include other NVM except the NAND 2252, for example,resistive RAM (ReRAM), phase change RAM (PRAM), or magnetic RAM (MRAM),or a magnetic storage medium or an optical storage medium, or the like.

The DRAM 2253 may be used as a buffer memory. For example, the DRAM 2253may be double data rate (DDR) SRAM (DDR SDRAM), low power DDR (LPDDR)SDRAM, graphics DDR (GDDR) SDRAM, rambus DRAM (RDRAM), or high bandwidthmemory (HBM). However, the present inventive concept is not limitedthereto, and the storage device 2250 may use a volatile memory (VM) oran NVM other than DRAM as a buffer memory. The DRAM 2253 may temporarilystore (e.g., buffer) data to be programmed in the NAND 2252 or data readfrom the NAND 2252.

The storage server 2200 may further include a switch 2230 and the NIC2240. The switch 2230 may selectively connect the processor 2210 to thestorage device 2250, or may selectively connect the NIC 2240 to thestorage device 2250, according to the control of the processor 2210. Inan embodiment of the inventive concept, the processor 2210 and the NIC2240 may be integrated into one body. In an embodiment of the inventiveconcept, the storage device 2250 and the NIC 2240 may be integrated intoone body.

The storage devices 2150, 2150 n, 2250, and 2250 m may correspond to thememory systems 10 and 20 described above with reference to FIGS. 1through 16. For example, the CTRL 2251 may transmit the command CMD andthe address ADDR to the NAND 2252 in the PAM-4 method according to arequest provided by one of the processors 2110, 2110 n, 2210, and 2210m. In this case, the NAND 2252 may sample the command CMD and theaddress ADDR in the PAM-4 mode. The CTRL 2251 may transmit the data DATAto the NAND 2252 in the NRZ method. In this case, the NAND 2252 maysample the data DATA in the NRZ mode.

While the inventive concept has been particularly shown and describedwith reference to embodiments thereof, it will be understood thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A memory system, comprising: a memory controller configured to transmit a command, an address, or data to a first channel based on a data input/output signal having one of N (N is a natural number of three or more) different voltage levels during a first time interval, the memory controller configured to transmit the command, the address, or the data not transmitted during the first time interval to the first channel based on the data input/output signal having one of two different voltage levels during a second time interval; and a memory device configured to sample the data input/output signal received via the first channel during the first time interval in a pulse amplitude modulation (PAM)-N mode, the memory device configured to sample the data input/output signal received via the first channel during the second time interval in a non return to zero (NRZ) mode.
 2. The memory system of claim 1, wherein the memory controller transmits the command and the address to the first channel during the first time interval, and the data to the first channel during the second time interval.
 3. The memory system of claim 2, wherein the memory controller is further configured to transmit a command latch enable signal in an enable state to the first channel as the data input/output signal including the command is transmitted to the first channel, and transmit an address latch enable signal in the enable state as the data input/output signal including the address is transmitted to the first channel, wherein the memory device operates in the PAM-N mode when the command latch enable signal or the address latch enable signal is in the enable state, and operates in the NRZ mode when each of the command latch enable signal and the address latch enable signal is in a disable state.
 4. The memory system of claim 2, wherein the memory controller is further configured to transmit a data input/output signal enable signal (DQ enable signal) having one of first through fourth voltage levels to the first channel as the data input/output signal is transmitted to the first channel, wherein the memory device operates in the PAM-N mode when the DQ enable signal received via the first channel has the first voltage level indicating the command or the second voltage level indicating the address, and operates in the NRZ mode when the DQ enable signal has the third voltage level indicating the data.
 5. The memory system of claim 2, wherein the memory controller is configured to transmit a write enable signal in a toggle state to the first channel as the data input/output signal including the command or the address is transmitted to the first channel, wherein the memory device operates in the PAM-N mode when the write enable signal is in the toggle state, and operates in the NRZ mode when the write enable signal is in a toggle-off state.
 6. The memory system of claim 2, wherein the memory controller is further configured to transmit a data strobe signal in a toggle state to the first channel as the data input/output signal including the data is transmitted to the first channel, wherein the memory device operates in the PAM-N mode when the data strobe signal is in a toggle-off state, and operates in the NRZ mode when the data strobe signal is in the toggle state.
 7. The memory system of claim 1, wherein the memory controller transmits the data to the first channel during the first time interval, and transmits the command and the address to the first channel during the second time interval.
 8. The memory system of claim 7, wherein the memory controller is further configured to transmit a command latch enable signal in an enable state to the first channel as the data input/output signal including the command is transmitted to the first channel, and transmit an address latch enable signal in the enable state to the first channel as the data input/output signal including the address is transmitted to the first channel, wherein the memory device operates in the NRZ mode when the command latch enable signal or the address latch enable signal is in the enable state, and operates in the PAM-N mode when each of the command latch enable signal and the address latch enable signal is in a disable state.
 9. The memory system of claim 7, wherein the memory controller is further configured to transmit a data input/output signal enable signal (DQ enable signal) having one of first through fourth voltage levels to the first channel as the data input/output signal is transmitted to the first channel, wherein the memory device operates in the NRZ mode when the DQ enable signal has the first voltage level indicating the command or the second voltage level indicating the address, and operates in the PAM-N mode when the DQ enable signal has the third voltage level indicating the data.
 10. The memory system of claim 1, wherein the memory controller is further configured to transmit a mode setting signal to the first channel, and the memory device operates in the PAM-N mode or the NRZ mode according to the mode setting signal.
 11. The memory system of claim 1, wherein the memory controller comprises: a bit splitter configured to split bits of the command, the address, or the data into M-bits (M is a natural number of two or more); a pre-processing circuit configured to generate first through M^(th) bits by pre-processing the M bits output by the bit splitter in the PAM-N mode or the NRZ mode; and first through M^(th) drivers configured to generate the data input/output signal having one of first through N^(th) voltage levels based on the first through M^(th) bits.
 12. The memory system of claim 11, wherein the pre-processing circuit generates the first through M^(th) bits corresponding to one of the first through N^(th) voltage levels in the PAM-N mode, and generates the first through M^(th) bits corresponding to the first and N^(th) voltage levels in the NRZ mode.
 13. The memory system of claim 1, wherein the memory device further comprises: first through (N−1)^(th) sense amplifiers configured to output first through (N−1)^(th) comparison results by comparing a voltage level of the data input/output signal to each of first through (N−1)^(th) reference voltages in the PAM-N mode, and output the first through (N−1)^(th) comparison results by comparing the voltage level of the data input/output signal to a one reference voltage of the first through (N−1)^(th) reference voltages in the NRZ mode; an output decoder configured to output M bits by performing decoding based on the first through (N−1)^(th) comparison results; and a register circuit configured to output the M bits output by the output decoder as the command, the address, or the data in the PAM-N mode, and output one bit of the M bits output by the output decoder as the command, the address, or the data in the NRZ mode.
 14. The memory system of claim 13, wherein the first through (N−1)^(th) sense amplifiers output as a value of each of remaining comparison results except for a comparison result corresponding to the one reference voltage among the first through (N−1)^(th) comparison results in the NRZ mode.
 15. The memory system of claim 1, wherein the memory device comprises a memory cell array including memory cells connected to a plurality of word lines and a plurality of bit lines for storing the data, and each of the memory cells comprises a NAND flash memory cell.
 16. A memory device, comprising: a receiver configured to output M bits (M is a natural number of two or more) corresponding to a voltage level of a data input/output signal received via a data input/output signal pin (DQ pin) based on first through (N−1)^(th) (N is a natural number of three or more) reference voltages in a pulse amplitude modulation (PAM)-N mode, and output one bit corresponding to the voltage level of the data input/output signal based on a certain reference voltage of the first through (N−1)^(th) reference voltages in a non return to zero (NRZ) mode; and a control logic circuit configured to control the receiver in the PAM-N mode or the NRZ mode based on a symbol type of the data input/output signal corresponding to one of a command, an address, and data.
 17. The memory device of claim 16, wherein the control logic circuit controls the receiver in the PAM-N mode when a command latch enable signal (CLE) received via a CLE pin or an address latch enable signal (ALE) received via an ALE pin is in an enable state, and controls the receiver in the NRZ mode when each of the CLE and the ALE is in a disable state.
 18. The memory device of claim 16, wherein the control logic circuit controls the receiver in the NRZ mode when a command latch enable signal (CLE) received via a CLE pin or an address latch enable signal (ALE) received via an ALE pin is in an enable state, and controls the receiver in the PAM-N mode when each of the CLE and the ALE is in a disable state.
 19. The memory device of claim 16, wherein the receiver comprises: first through (N−1)^(th) sense amplifiers configured to output first through (N−1)^(th) comparison results by comparing a voltage level of the data input/output signal to each of the first through (N−1)^(th) reference voltages in the PAM-N mode, and output the first through (N−1)^(th) comparison results by comparing the voltage level of the data input/output signal to the certain reference voltage in the NRZ mode; an output decoder configured to output M bits by performing decoding based on the first through (N−1)^(th) comparison results; and a register circuit configured to output the M bits output by the output decoder as the command, the address, or the data in the PAM-N mode, and output one bit of the M bits output by the output decoder as the command, the address, or the data in the NRZ mode.
 20. A memory system, comprising: a memory controller configured to transmit to a first channel a data input/output signal having one of two different voltage levels or the data input/output signal having one of N (N is a natural number of three or more) different voltage levels, according to a symbol type of the data input/output signal corresponding to one of a command, an address, and data; and a memory device configured to sample the data input/output signal in a non return to zero (NRZ) mode or a pulse amplitude modulation (PAM)-N mode according to the symbol type of the data input/output signal received via the first channel. 